Is it fine to sleep in a painted room after 3 days?

If there are no discernible odors or fumes, Good Night! It should be perfectly okay.

Most house paints in use today are latex based and any smell is not toxic to begin with. Oil based or lead containing paints used decades ago may have been, but these are exceedingly hard to obtain today so I don't see much chance you used one. Other than the irritation from the smell, you could sleep there day 1.